Cherenkov imaging of Total Skin Electron Therapy (TSET) Abstract Whole-body skin electron radiotherapy has been clinically demonstrated to be effective to treat mycosis fungoides. However, due to setup positioning uncertainties and potential patient movements during total skin electron therapy (TSET), dose delivered to the patient skin tissue can deviate from dose prescription. Cherenkov emission from tissue has recently been demonstrated, providing a mapping related to the radiation delivery to skin tissue. The signal is optimally captured by time-gated intensified cameras, synchronized to the linear accelerator pulses, allowing rejection of the majority of background room light, and providing real time video of each radiotherapy treatment with high dose rates. The implementation of Cherenkov imaging offers an excellent technology to detect abnormalities in the treatment, which would otherwise go unnoticed. This proposal seeks to advance this technology as a verification tool through a clinical trial to monitor the daily treatment delivery of TSET patients and develop proper corrections that can be applied to the acquired signal to ensure it is quantitatively accurate in documenting delivered skin dose. Three of the most dominant factors, which alter the linearity between dose and Cherenkov signal, are the corrections for perspective direction, tissue curvature, and tissue optical properties. These important corrections are quantified in this pilot study of TSET, in partnership with DoseOptics LLC, the company that developed the Cherenkov imaging technology for radiation verification, to perfect technology for daily monitoring of radiation delivery. We will compare the dosimetry accuracy of Cherenkov imaging by comparing measurements in-vivo at 9 locations using diode, OSLD, and Scintillator detectors. In addition, we will perform measurements in optical phantoms of known tissue optical properties at TSE treatment conditions and Monte-Carlo simulation studies to quantity the three correction factors. We will also develop techniques to overlay skin dose obtained from corrected Cherenkov image to patient-specific surface anatomy based on surface 3D body contour data obtained before TSE treatment to assess the actual skin dose distribution for daily TSE treatment. Taking together, this project will advance on the most compelling systems for radiotherapy imaging in decades. The core of the project is combined technology systems, testing the utility in the setting of TSET.